Initial pass at new host ABI #7795
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| length: usize, | ||
| ret: *anyopaque, | ||
| ops: *RocOps, | ||
| }; |
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This is a bit different from how we're doing it in the Rust compiler. Some notes:
- To avoid needing to get into the C calling convention at all, I continued using the "all functions take a single pointer and return
void" thing withroc_allocand friends.- The one exception is that I have them all take a second argument, the "env pointer" that's a pointer to whatever the host wants it to be - e.g. a pointer to an arena in case the host wants to use arena allocation for everything.
- Since this is now different enough from the signature for something like
malloc, I figured it would be fine to require that the host handle OOM itself rather than the Roc compiler generating an extra conditional to detect null and callroc_crashedif so. (All the hosts that anyone will use as templates to copy from will do this anyway, so I don't think it will be a problem.)
| /// but it is *not* guaranteed to be null-terminated. | ||
| pub const RocDbg = struct { | ||
| // TODO make this be structured instead of just a string, so that | ||
| // the host can format things more nicely (e.g. syntax highlighting). |
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I figure we can do the "structured dbg" and "structured expect failure" in a future PR. This is enough to unblock Hello World.
src/host_abi.zig
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| /// very simple; the calling convention is just "pass a single pointer". | ||
| pub const RocCall = struct { | ||
| /// Function pointers that the Roc program uses, e.g. alloc, dealloc, etc. | ||
| ops: *RocOps, |
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This ops pointer is what will actually get threaded through from one Roc function call to another behind the scenes.
arg and ret only get used in the outermost function wrapper that the host calls.
This means that having all of these be pointers is a minimal cost, because all of them except for ops will only get dereferenced once per host call.
rtfeldman
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Co-authored-by: Brendan Hansknecht <[email protected]> Signed-off-by: Richard Feldman <[email protected]>
Co-authored-by: Andrew Kelley <[email protected]> Signed-off-by: Richard Feldman <[email protected]>
| @@ -65,7 +65,7 @@ pub fn RocOps(comptime CallEnv: type, comptime HostFns: type) type { | |||
| /// If it cannot provide a non-null pointer (e.g. due to OOM), it | |||
| /// must not return, and must instead do something along the lines | |||
| /// of roc_crashed. | |||
| pub const RocAlloc = struct { | |||
| pub const RocAlloc = extern struct { | |||
| alignment: usize, | |||
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Not sure if this helps here since the struct has no padding, but in Zig std lib we've started using an Alignment type that stores the log2 value. It's pretty handy because you only need 6 bits to describe any alignment for a 64-bit address.
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Nice, that's a cool trick! I agree that it probably doesn't help here, but that's a good one to know for future reference. 🤘
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